Process for manufacturing a fuel tank equipped with an internal accessory

ABSTRACT

Process for manufacturing a fuel tank equipped with an internal accessory and having a plastic wall produced from a parison, said process comprising, in order, the following steps: a) the accessory ( 2 ) and the molten parison ( 5 ) are introduced a mould ( 1 ) so that the accessory ( 2 ) is surrounded by the parison ( 5 ), said mould comprising cavities ( 1 ) equipped with at least one moving part ( 4 ); b) a pressurized gas is introduced inside the parison ( 5 ) to carry out a pre-blow moulding of said parison; c) the pre-blow-moulded parison ( 5 ) is pressed locally against the accessory ( 2 ) using the moving part ( 4 ) in order to firmly attach the two without piercing the parison ( 5 ); d) the mould ( 1 ) is closed and the final blow moulding of the parison ( 5 ) is carried out by flattening it against the mould ( 1 ) cavities using the pressurized gas; and e) the tank is removed from the mould ( 1 ).

The present invention relates to a process for manufacturing a fuel tankequipped with an internal accessory and in particular a noise reductionbaffle.

Fuel systems on board vehicles of various types generally comprise atank for storing fuel, and this tank generally comprises at least oneinternal component. Conventionally, in the case of plastic tanksobtained by extrusion-blow moulding, such a component is introduced intoand attached to the tank, after the manufacture of the latter, throughan opening made in the wall of the tank. However, the penetrationthrough the wall of the tank must take into account the sealingrequirements laid down by current environmental standards (LEV II andPZEV for example). For this purpose, the reduction in the number andsize of the openings in the wall of the tank constitutes a favourablefactor in reducing evaporative losses.

One particular case of such accessories is that of noise reductionbaffles, the purpose of which is to absorb the noise (“slosh” noise)associated with the waves which may be generated inside the tank whenthe vehicle accelerates rapidly, brakes, turns, etc. Such baffles arealso known as anti-slosh baffles in the jargon of the field.

In order to solve the problem of attaching them to the inside of a tankwithout having to make an opening/cut therein, it is known to introducethem into the tank at the same time as it is manufactured by extrusionof a tubular parison around such a baffle, and then by blow moulding theparison and by attaching the baffle to this parison.

In such a process, the baffle may be attached to the parison after orbefore blow moulding of this parison.

One process according to the 1^(st) alternative is described inApplication EP 103832 and comprises the following steps:

-   -   extrusion of a tubular parison around a baffle held by a support        pin;    -   piercing the parison with a mandrel that is firmly attached to        the mould and that takes on the role of a support;    -   withdrawal of the support pin;    -   blow moulding of the parison;    -   attachment of the baffle to the blow-moulded parison using the        mandrel;    -   withdrawal of the mandrel and demoulding of the tank.

This process therefore has the disadvantage that the parison is piercedoutside of the parting line and therefore has an opening which must beresealed in a leaktight manner after demoulding of the tank. The processdescribed in Application JP 6143396 makes it possible to solve thisproblem by arranging to attach the baffle to the parison by weldingbefore blow moulding of the parison, specifically due to moving parts inthe mould cavities. This process however has the disadvantage that theinternal volume of the tank is limited around the baffle since thisbaffle is welded before blow moulding and therefore limits the expansionof the parison in its vicinity. Similarly, the size of the baffle islimited by the volume of the extruded parison (which is smaller thanthat of the blow-moulded tank).

The present invention aims to solve these problems by providing aprocess in which the attachment of the baffle (or of another internalaccessory) to the parison takes place without piercing/cutting of theparison, does not necessarily lead to a restriction of the tank volumearound the baffle and allows the insertion of a large-sized (andtherefore more effective) baffle.

For this purpose, the present invention relats to a process formanufacturing a fuel tank equipped with an internal accessory and havinga plastic wall produced from a parison, said process comprising, inorder, the following steps:

-   -   a) the accessory and the molten parison are introduced into a        mould so that the accessory is surrounded by the parison, said        mould comprising cavities equipped with at least one moving        part;    -   b) a pressurized gas is introduced inside the parison to carry        out a pre-blow moulding of said parison;    -   c) the pre-blow-moulded parison is pressed locally against the        accessory using the moving part in order to firmly attach the        two without piercing the parison;    -   d) the mould is closed and the final blow moulding of the        parison is carried out by flattening it against the mould        cavities using the pressurized gas; and    -   e) the tank is removed from the mould.

The term “accessory” is understood within the context of the inventionto mean a component or a set of components having an active role in thetank such as to ventilate, to convey fuel to the engine, to measure theliquid level, to reduce the noise linked to waves, etc. In particular,it is a noise reduction baffle such as described previously. Preferably,this baffle is made of plastic and most particularly preferably, it isbased on the same plastic as that forming the parison (and therefore thetank which is moulded from it). It is therefore, advantageously, abaffle made of high-density polyethylene (HDPE): sec below.

The expression “fuel tank” is understood to mean a leakproof tank, ableto store fuel under diverse and varied usage and environmentalconditions. An example of this tank is that with which motor vehiclesare fitted.

The fuel tank according to the invention is made with a plastic wall,generally comprising an internal face on its concave part and anexternal face on its convex part.

The term “plastic” is understood to mean any material comprising atleast one synthetic polymer resin.

Any type of plastic may be suitable. Particularly suitable plasticsbelong to the category of thermoplastics.

The term “thermoplastic” is understood to mean any thermoplasticpolymer, including thermoplastic elastomers, and also blends thereof.The term “polymer” is understood to mean both homopolymers andcopolymers (especially binary or ternary copolymers). Examples of suchcopolymers are, non-limitingly: random copolymers, linear blockcopolymers, other block copolymers and graft copolymers.

Any type of thermoplastic polymer or copolymer, the melting point ofwhich is below the decomposition temperature, is suitable. Syntheticthermoplastics having a melting range spread over at least 10 degreesCelsius are particularly suitable. Examples of such materials includethose that exhibit polydispersion in their molecular weight.

In particular, it is possible to use polyolefins, thermoplasticpolyesters, polyketones, polyamides and copolymers thereof. A blend ofpolymers or copolymers may also be used similarly it is also possible touse a blend of polymeric materials with inorganic, organic and/ornatural fillers such as, for example, but non-limitingly: carbon, saltsand other inorganic derivatives, natural or polymeric fibres. It is alsopossible to use multilayer structures composed of stacked and joinedlayers comprising at least one of the polymers or copolymers describedabove.

One polymer that is often used is polyethylene. Excellent results havebeen,obtained with high-density polyethylene (HDPE).

Preferably, the tank for which the process according to the invention isintended has a multilayer structure comprising at least onethermoplastic layer and at least one additional layer which,advantageously, may be formed from a material that is a barrier toliquids and/or gases.

Preferably, the nature and the thickness of the barrier layer are chosenso as to minimize the permeability of the liquids and gases in contactwith the wall of the tank. Preferably, this layer is based on a barriermaterial, i.e. a fuel-impermeable resin such as, for example, EVOH (apartially hydrolysed ethylene/vinyl acetate copolymer). Alternatively,the tank may be subjected to a surface treatment (fluorination orsulphonation) for the purpose of making it impermeable to the fuel.

The term “parison” is understood to mean a preform of a single part,generally extruded and generally of substantially tubular shape, whichis intended to form the wall of the tank after moulding, i.e. after anoperation which consists in forming the parison, which is in the meltstate, into the required shapes and dimensions using the mould in orderto obtain a tank.

The process according to the invention preferably uses an extrudedparison. This parison may be derived from an extruder with a storagehead, in which case the process generally uses a mould that is fixedopen at the start of each cycle in order to receive a parison.Alternatively, the process may resort to continuous extrusion, eitherwith a moving mould that is periodically closed up over this parison, orwith a manipulation of the parison towards the mould.

According to the invention, the parison and the accessory are placed ina mould, the accessory being surrounded by the (preferably stretched)parison. Generally, this takes place either by inserting the accessoryinto the parison that is held apart by an appropriate device, or byextruding the parison around the accessory while separating it with adevice that follows its movement on exiting the extruder. The lattervariant is preferred, most particularly in combination with an extruderwith a storage head.

Whichever variant is used, the process according to the inventiontherefore preferably uses a tool that makes it possible to stretch theparison (keep it open). This tool may consist of clamps or jaws capableof gripping the edges of the parison and keeping them apart. Preferably,this tool is operated by a robot.

The process according to the invention also uses a mould that comprisescavities, i.e. sorts of hollow half-shells, the perimeters of which areidentical and the internal surface of which is equipped with a reliefthat corresponds to the external shape of the tank, the tank beingmoulded by pressing the parison against this surface using a pressurizedgas injected into the parison, generally by means of a blow pin.

According to the invention, the mould cavities comprise at least onemoving part capable of locally pressing the parison against theaccessory in order to attach the latter thereto. This attachment may becarried out by welding, mechanical anchoring, snap riveting, etc.Preferably, when the materials of the accessory and of the parison arecompatible (at least at the surface), this attachment takes place bywelding.

Generally, when the mould is open (i.e. when its cavities areseparated), the moving part projects into the mould. When it is closed,the moving part pushes the parison and comes into contact with thecomponent; it then remains in place so that it is retracted inside themould in order that its end can conform to (form the continuation of)the internal surface of the cavity on which it is found when the mouldis closed.

This moving part is preferably a type of rod for which the movement andthe pressure that it exerts on the parison at the location of itsattachment to the accessory are controllable.

Preferably, there are several moving parts distributed so as to attachthe accessory to the tank in a balanced manner (i.e. to ensure thatstress concentrations during operation are avoided).

In the process according to the invention, in particular when theattachment of the accessory takes place by welding, the accessory ispreferably preheated prior to its placement in the parison, saidpreheating taking place preferably at least in the zones intended forits attachment to the parison.

In the process according to the invention, the accessory is preferablyloaded onto a support prior to its placement in the parison. Generally,this loading is automated (carried out by a robot or a carousel-typedevice). This support may be a blow pin which may be used to introducethe pressurized gas (preferably air) into the parison at least duringthe pre-blow-moulding step b). Preferably, the support for the baffledoes not carry out another role so that it can be withdrawn beforeclosure of the mould for the final blow moulding of the tank.

During step b), the parison is simply pre-blow moulded/inflated,preferably without contacting the mould cavities. The pre-blow mouldingof the parison simple consists therefore of an expansion of said parisonso that its “active” part (that clamped between the mould cavities andintended to form the tank after blow moulding) acquires substantiallythe same size (internal volume) as the tank, the final blow-mouldingstep (d) mainly serving to give it its final relief/shape. In general,at the end of step b), the internal volume of the working part of theparison is at least equal to 70%, preferably at least 80%, or even 90%,of the internal volume of the tank.

During this step, the mould is not closed and the lower and upper endsof the parison are preferably sealed in a leaktight manner, but withoutbeing closed (i.e. without having their edges welded but, on the otherhand, kept apart), by suitable devices located respectively underneathand on top of the mould. These sealing devices may consist of an innerblock and two outer moving parts that clamp the parison to the block.This type of device gives good results, in particular for the lowerdevice. As regards the upper device, this may be formed by the extrusionhead, i.e. in this variant, which is moreover advantageous, the parisonis not yet cut at the time of the pre-blow moulding but is stillconnected to the extrusion head. This variant makes it possible to dowithout the pre-blow moulding pin: this is because it is sufficient toequip the extrusion head with a blow-moulding device.

In this variant, the support for the accessory may therefore bewithdrawn after step c) and before step d) (final closure of the mouldand pressing of the pre-blow-moulded parison against its cavities togive it its final shape). In this variant, to carry out the blowmoulding in step d), it is possible to use at least one (preferably two)needle(s) that pierce(s) the parison during the closure of the mould,preferably in a zone that will subsequently be machined (for example, atthe openings for pump/gauge module(s)).

Alternatively, in another variant, during step d), the mould cavitiesare pressed against one another and clamp the parison between theirperimeters (which delimits a parting line around the perimeter of thetank) and around the blow pin which acts as a support for the accessoryduring steps a) to d) while being withdrawn before step e). Generally,the blow pin is inserted into the mould via the underside.

In this variant, the mould is therefore gradually closed between stepsb) and d), the rods projecting inside the mould that attach theaccessory in step c) then remaining immobile and preferably applying aconstant pressure to the attachment point(s) and being graduallywithdrawn inside the mould in order to conform to the internal surfaceof the cavities in step d).

In this variant, the pin therefore leaves an opening in the tank at theparting line (part clamped by the perimeters of the cavities). Thisopening may be resealed before demoulding of the tank, and preferablyimmediately after removal of the pin, by dint of an appropriate device(sorts of jaws) in the mould.

In the process according to the invention, before the demoulding stepe), the moulded parison is preferably left to cool—generally bycirculating a cooling gas through one or more blow-moulding needles. Themould cavities are then preferably also cooled by circulation of a fluidin a network of ducts.

At the end of the demoulding step and before the following mouldingcycle, it may prove necessary to clean (deflash) the intermediateparison-sealing devices which generally comprise parison “flash” orwaste that overflows from the mould when the latter is closed.

The process according to the invention is suitable for attaching anyaccessory to the inside of a fuel tank. It is however particularly wellsuited to attaching noise reduction baffles.

Preferably, these baffles have a suitable geometry in order to be ableto occupy a maximum of space in the tank once the latter is moulded. Inother words: they preferably have a variable geometry and occupy asmaller volume before blow moulding of the parison than when the tank isin operation.

Most particularly preferably, the variable geometry is obtained via thechoice of a baffle:

-   -   that comprises sliding parts, the deployment of which is carried        out during a subsequent finishing operation; or    -   that comprises two separate parts which are placed side by side        until the end of the pre-blow-moulding step b) and separated        just before step c); or    -   that has a foldable structure and that is in a folded-up form in        the parison before blow moulding of the latter.

Thus, in a first variant, the baffle comprises sliding parts (type of“drawers”), the deployment of which is carried out during a subsequentfinishing operation, which is either manual or automated, throughone/some opening(s) in the tank.

In a second variant which requires the presence of at least one movingpart in each cavity, the baffle comprises two separate parts, each borneby a holding pin. When the baffles are introduced into the parison (orwhen the parison is extruded around the baffle) these parts are placedside by side. The operation for separating the baffles takes place atthe end of the pre-blow-moulding step b) and just before the attachmentof the parts of the baffle to the parison via the moving parts of thecavities (step c)). These pins are preferably firmly attached to thelower sealing device of the parison.

And in a 3^(rd) variant, the baffle has a foldable structure (forexample of accordion type) and it is in a folded-up form in the parisonbefore blow moulding of the latter. Preferably, this structure isdeployed by compression on at least 2 of its points, which preferablycorrespond to the points for attachment of the baffle to the parison,using moving parts. This compression (and the resulting deployment) maybe carried out during the step of attaching the baffle to the parison(step c)) and/or during the closure of the mould to carry out the finalblow moulding (step d)). In this variant, the foldable structure may besuch that during its deployment, new points for attachment of theaccessory to the parison are created.

The objective of FIGS. 1 to 10 is to illustrate certain concrete aspectsof the invention, without wishing to restrict the scope thereof in anyway.

The objective of FIGS. 1 to 4 is to illustrate the principle of aprocess according to a variant of the invention;

FIGS. 5 and 6 illustrate a 1^(st) subvariant of this process variant;

FIGS. 7 to 9, a 2^(nd) subvariant; and finally,

FIGS. 10 and 11, a 3^(rd) subvariant.

These figures illustrate common components, namely:

-   1: a mould comprising two cavities;-   2: a noise reduction baffle;-   3: a support for the baffle;-   4: parts that move in the cavities;-   5: a parison;-   6: a device for separating and guiding the parison; and 7 & 7′: a    lower sealing device of the parison comprising an inner block (7)    and two outer moving parts (7′).

In FIG. 1, it can be seen how the device (6) guides the parison (5) inorder to introduce it around the baffle (2) while keeping it open/apart.The baffle (2) has been previously loaded onto a support (3). Thisdevice is operated by a robot and stops underneath the sealing device(7, 7′) as illustrated in FIG. 2. The mould cavities have an internalsurface (1′) that corresponds to the external surface of the tank to bemoulded.

In FIG. 2, it can be seen how the inner block (7) makes it possible toseparate the parison and to avoid contact between the baffle and theparison, and how the outer parts (7′) clamp the parison (5) to thisblock (7) so as to carry out a pre-blow moulding in a leaktight mannerusing the extrusion head (not represented), to which the parison isstill attached.

In FIG. 3, the mould (1) can be seen in an intermediate closure positionwhich is such that the moving parts (4) have locally pushed the parisonto bring it into contact locally with the baffle (2). Once the points ofcontact (welding in this variant) are produced, the baffle support (3)may be withdrawn (it is moreover no longer represented in this figure)and it is possible to close the mould (1) for the final moulding of thetank. During the closure, the moving parts (4) retract inside the mould(although they are immobile in absolute terms and keep the welding spotsunder pressure) and become flush with the surface of the cavities (1).

The blow-moulding needles (represented as dotted lines) then pierce theparison to carry out the blow-moulding operation.

The mould is shown closed in FIG. 4, where it can be seen that the mouldcavities are placed side by side over their perimeter. When the assemblyhas been cooled, the tank may be demoulded.

The baffle illustrated in FIGS. 1 to 4 is a “conventional”, voluminousand incompressible baffle.

The use of a baffle that has large dimensions when in service may befacilitated (reduction in the risk of contact between the parison andthe baffle before blow moulding) when the baffle is compressible (i.e.has larger dimensions when in service, in the tank, than when it isinserted into the parison). This is illustrated by 3 subvariants inFIGS. 5 to 10.

In a 1^(st) subvariant that is the subject of FIGS. 5 and 6, the baffle(2) comprises drawers (21) which are closed throughout the manufactureof the tank (FIG. 3), and which are opened (manually or automatically;cf. FIG. 4) during a subsequent finishing step and this being carriedout through one or more orifices. These may be openings for pump/gaugemodule(s) which are cut out on the finishing line and the location ofwhich is indicated in FIG. 3 by two solid arrows.

In a 2^(nd) subvariant that is the subject of FIGS. 7 to 9, the baffle(2) is in fact composed of two separate parts (22, 23) which are eachsupported by independent supports (3′, 3″) which are positioned side byside until the pre-blow moulding of the parison (see FIG. 7) and whichare separated (see FIG. 8) before attachment of the baffles (22, 23) bythe moving parts (4) (see FIG. 9 where horizontal arrows show themovement of these parts and vertical arrows show the withdrawal movementof the supports).

In a 3^(rd) subvariant that is the subject of FIGS. 10 and 11, thebaffle (2) is composed of a foldable structure, a radial view (through aplane perpendicular to the axis of the parison) of which is illustratedin FIG. 10.

This structure comprises two end zones (24, 25) which act as points ofcompression for the moving parts (4) of the mould during step c) or evenduring the subsequent closure of the mould. This is illustrated by thecentral arrows in FIG. 11, which represents an axial cross section ofthe moulded tank with its walls “ghosted out”. The closure of the mould(not represented) creates additional attachment points (illustrated bythe side arrows in FIG. 11).

In order to avoid shell damage during burst/drop test (and of course, inreal life, in the case of crash), it is prefeable to provide at leastone weak point (notch) around the weld zones (i.e. the points where thebaffle and the tank are joined by the moving part inside the mould).According to a preferred embodiment, the weld zones are equipped withweld feet and there is a break zone (weak point) provided between saidweld feet and the body of the accessory so that in the case ofdrop/crash, the accessory can eventually be detached from the tankwithout damaging it. Such a feature is for instance disclosed in patentapplication US 2003/0201021, the content of which is incorporated byreference into the present application.

Also, since the accessory is generally cold when it is attached to themolten parison and since said parison generally retracts afterwardsduring cooling, it is preferable to provide the accessory with anappropriate design so that said retraction does not damage the tankand/or break the above mentioned break zones (weak points). Providingparts in the accessory with an appropriate thickness and shape so thatthey are flexible and can easily be deformed, gives good results.

FIG. 12 illustrates the above mentioned features, namely: weld feet(26), a notch zone (27) and parts with improved flexibility (28).

1. Process for manufacturing a fuel tank equipped with an internalaccessory and having a plastic wall produced from a parison, saidprocess comprising, in order, the following steps: a) the accessory andthe molten parison are introduced into a mould so that the accessory issurrounded by the parison, said mould comprising cavities equipped withat least one moving part; b) a pressurized gas is introduced inside theparison to carry out a pre-blow moulding of said parison; c) thepre-blow-moulded parison is pressed locally against the accessory usingthe moving part in order to firmly attach the two without piercing theparison; d) the mould is closed and the final blow moulding of theparison is carried out by flattening it against the mould cavities usingthe pressurized gas; and e) the tank is removed from the mould. 2.Process according to the preceding claim, in which the parison isextruded around the accessory while being guided and kept open(separated) using a device that follows its movement on exiting theextruder.
 3. Process according to the preceding claim, in which theextruder comprises a storage head.
 4. Process according to any one ofthe preceding claims, in which when the mould is open (i.e. when itscavities are separated), the moving part projects into the mould andwhen it is closed, the moving part does not move so that it is retractedinside the mould in order that its end can conform to (form thecontinuation of) the internal surface of the cavity on which it is foundwhen the mould is closed.
 5. Process according to any one of thepreceding claims, in which during the pre-blow-moulding step b) thelower and upper ends of the parison are sealed in a leaktight manner,but without being welded, by suitable devices located respectivelyunderneath and on top of the mould.
 6. Process according to any one ofthe preceding claims, characterized in that during step d) the mouldcavities are pressed against one another and clamp the parison around ablow pin which acts as a support for the accessory during steps a) to d)while being withdrawn at the end of step d), and in that when the pin iswithdrawn, it leaves an opening in the parison which is resealed beforestep e) by an appropriate device on the mould.
 7. Process according toany one of claims 1 to 5, characterized in that the accessory is held inthe parison by a support which is withdrawn after step c) and beforestep d).
 8. Process according to any one of the preceding claims, inwhich the accessory is a noise reduction baffle.
 9. Process according tothe preceding claim, characterized in that the baffle has a variablegeometry and occupies a smaller volume before blow moulding of theparison than when the tank is in operation.
 10. Process according to thepreceding claim, characterized in that the variable geometry is obtainedvia the choice of a baffle: that comprises sliding parts, the deploymentof which is carried out during a subsequent finishing operation; or thatcomprises two separate parts which are placed side by side until the endof the pre-blow-moulding step b) and separated just before step c); orthat has a foldable structure and that is in a folded-up form in theparison before blow moulding of the latter.